Role of n-dopant based electron injection layer in n-doped organic light-emitting diodes and its simple alternative

Young Wook Park, Jin Hwan Choi, Tae Hyun Park, Eun Ho Song, Hakkoo Kim, Hyun Jun Lee, Se Joong Shin, Byeong Kwon Ju, Won Jun Song

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


We investigate the enhancement mechanism of the electroluminescence (EL) of alkali metal based n-doped organic light-emitting diodes (OLEDs). The dual role of the n-dopant (carrier transport and lowering of the injection barrier) induces a trade-off. When the electron transport layer (ETL) is optimally doped by the n-dopant for the highest conductivity, the amount of n-dopant at the ETL/cathode interface is insufficient to form enough chemical bonds with the cathode for efficient carrier injection. This insufficient amount of n-dopant limits the carrier injection properties. To solve this problem, we demonstrated that the addition of an electron injection layer (EIL) comprised of the n-dopant could increase its presence at the interface and, thereby, improve the carrier injection properties and, consequently, the EL efficiency. Moreover, simply using an alkali-metal alloy (rather than co-deposition) on the n-doped ETL as a cathode, instead of using the additional EIL, greatly improves the EL efficiency of the OLEDs. The alkali-metal alloy cathode increased the interfaced states at the ETL/cathode. The proposed model was confirmed by x-ray photoemission spectroscopy experiments on the alkali-metal n-dopant/electrode interface.

Original languageEnglish
Article number013312
JournalApplied Physics Letters
Issue number1
Publication statusPublished - 2012 Jan 2

Bibliographical note

Funding Information:
This work was supported by a Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea Ministry of Education, Science and Technology (MEST) (CAFDC-20100009869) and by the World Class University (WCU, R32-2008-000-10082-0) Project of MEST, as well as by the Industrial Strategic Technology Development Program of MKE (KI002104, Development of Fundamental Technologies for Flexible Combined-Function Organic Electronic Device). We also wish to thank the Korea Basic Science Institute for the use of their XPS equipment.

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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